Arggh! Not the dreaded "cat a single file into a pipe" command!
This can always be replaced more efficiently by simply redirecting STDIN on the recieving command. Thus the example becomes
$ tr -d "\r" < dosfile.txt > unixfile.txt
which saves (approximately :) one process and two file handles.
Of course, if you've got two files, you simply can't do this. And if the pipeline command is being generated from a script, the ease of building it this way may outway the efficiency of avoiding the extraneous "cat" | 